Siemens Argus 7SR21 - Inrush Restraint (81 HBL2); Figure 5.6-2 Logic Diagram: Close Circuit Supervision Feature (74 CCS); Figure 5.7-1 Logic Diagram: Harmonic Block Feature (81 HBL2)

7SR210 & 7SR220 Description of Operation
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Figure 5.6-2 Logic Diagram: Close Circuit Supervision Feature (74CCS)
5.7 Inrush Restraint (81HBL2)
Inrush restraint detector elements are provided, these monitor the line currents.
The inrush restraint detector can be used to block the operation of selected elements during transformer
magnetising inrush conditions.
The 81HBL2 Bias setting allows the user to select between Phase, Sum and Cross methods of measurement:
Phase Each phase is inhibited separately.
Sum With this method the square root of the sum of the squares of the second harmonic in each
phase is compared to each operate current individually.
Cross All phases are inhibited when any phase detects an inrush condition.
An output is given where the measured value of the second harmonic component is above the 81HBL2 setting.
Figure 5.7-1 Logic Diagram: Harmonic Block Feature (81HBL2)